Head mounted displays (HMDs), which are used while worn on the head to place a video screen in front of each eye of the user, find applications in various fields including the field of virtual reality. Typical HMDs are designed in the shape of a frame of goggles or large glasses that block but outside light and force the user to see only the HMD's pictures. With an HMD used, the user can view images irrespective of the direction he or she faces but then again it gives the user visual isolation from the surrounding environment.
In recent years, small image display devices have been proposed that allow users to view images along with the surrounding environment by means of presenting the images in a certain part of the field of vision. Such image display devices are not designed for image presentation only. Instead, the main purpose of it is to aid the everyday life. Images that are displayed are letters and numeric characters unlike the conventional HMDs.
For example, Japanese patent laid-open document (JP-A-7-209600) proposes an image display device having a liquid crystal display (LCD), a reflecting mirror, an ocular lens and other components contained within a single housing which is attached to a glasses or sunglasses frame. The housing is placed on top of either right or left lens of the glasses over the outside surface of it. An image that is displayed on the LCD is directed to one eye of the user in a diagonal down direction through the reflecting mirror, the ocular lens, and the lens of the glasses.
The image display device disclosed in the aforementioned reference is designed so that it is attached to the glasses, which spoils its appearance. Therefore, the use of an image display device as above in everyday life gives a strong impression of something strange to those around the user.
An object of the present invention is to provide an image display device of the type used while worn on the head without giving a strange impression when used in everyday life.